Display screen or portion thereof with a transitional graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a transitional graphical user interface, showing our new design and depicting a first image of the transitional graphical user interface.

FIG. 2 is a front view depicting a second image of the transitional graphical user interface.

FIG. 3 is a front view depicting a third image of the transitional graphical user interface.

FIG. 4 is a front view depicting a fourth image of the transitional graphical user interface.

FIG. 5 is a front view depicting a fifth image of the transitional graphical user interface.

FIG. 6 is a front view depicting a sixth image of the transitional graphical user interface.

FIG. 7 is a front view depicting a seventh image of the transitional graphical user interface.

FIG. 8 is a front view depicting an eighth image of the transitional graphical user interface.

FIG. 9 is a front view depicting a ninth image of the transitional graphical user interface; and,

FIG. 10 is a front view depicting a tenth image of the transitional graphical user interface.

The appearance of the transitional graphical user interface sequentially transitions between the images shown in FIGS. 1-10. The process or period in which one image transitions to another image forms no part of the claimed design.

The broken line showing of the display screen illustrates environmental structure, and the broken lines form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a transitional graphical user interface, as shown and described. 